Arm: Add read_description read funcs and use in GDB

Arm: Add read_description read funcs and use in GDB

Switch the Arm target to get target descriptions via arm_read_description
and aarch32_read_description, in the same style as other feature targets.
Add an enum to specify the different types - this will also be of use to
gdbserver in a later patch.

Under the hood return the same existing pre-feature target descriptions.

gdb/ChangeLog:

	* Makefile.in: Add new files.
	* aarch32-tdep.c: New file.
	* aarch32-tdep.h: New file.
	* aarch64-linux-nat.c (aarch64_linux_nat_target::read_description):
	Call aarch32_read_description.
	* arch/aarch32.c: New file.
	* arch/aarch32.h: New file.
	* arch/arm.c (arm_create_target_description)
	(arm_create_mprofile_target_description): New function.
	* arch/arm.h (arm_fp_type, arm_m_profile_type): New enum.
	(arm_create_target_description)
	(arm_create_mprofile_target_description): New declaration.
	* arm-fbsd-tdep.c (arm_fbsd_read_description_auxv): Call
	read_description functions.
	* arm-linux-nat.c (arm_linux_nat_target::read_description):
	Likewise.
	* arm-linux-tdep.c (arm_linux_core_read_description): Likewise.
	* arm-tdep.c (tdesc_arm_list): New variable.
	(arm_register_g_packet_guesses): Call create description functions.
	(arm_read_description) (arm_read_mprofile_description): New
	function.
	* arm-tdep.h (arm_read_description)
	(arm_read_mprofile_description): Add declaration.
	* configure.tgt: Add new files.